Dear John: A well-known investment adviser is promoting a video on his Web site predicting an apocalyptic collapse of the dollar within the next few years, leading to soaring prices, food riots and widespread civil unrest.

He says that this scenario will unfold when the dollar stops being the world’s reserve currency. This adviser argues that the reason for the impending collapse is that the federal debt, which has been grossly underreported, is so large that these events are almost inevitable.

I’m very skeptical. Some of this guy’s arguments make sense; others seem like hype to get the listener to subscribe to his newsletter.

Is there validity to this adviser’s warnings? S.E

Dear S.E. Wow, you want me to make a prediction about the end of the US as we know it! And here I am still trying to figure out who’ll win the Super Bowl.

Yes, the US federal debt is bigger than anyone is letting on. And, yes, if you include all the obligations under Social Security and Medicare, the situation is even worse.

Do I think all this is bad? Yes. And I’m particularly worried that Fed Chairman Ben Bernanke seems to have little concern that his wanton printing of money will make our currency and our economy weaker for years.

Perhaps all of this will even change the status of the US in the world financial community. I’m also worried about inflation and China’s ascent as an economic power.

However, the US is still the world’s biggest economy. And other nations still depend on us for money and security.

Diversification is still the best answer for normal investors — own some stocks, bonds, gold and have an ample supply of Campbell’s soup in the basement just in case this country’s financial situation hits the skids or we have another blizzard.

Meanwhile, cheer up. You’re depressing me.

Dear John: I retired from my job with the Port Authority Police in 2006 at age 61.

I had United Healthcare through a union contract and I was quite satisfied with it. Five dollar co-pays for visits to the doctor, $2 co-pays for generic prescription drugs and $5 for name-brand drugs.

When I turned 65 my former job informed me that by the end of that month I must enroll in Medicare, with United Healthcare becoming my secondary coverage.

I am not yet on Social Security, so I pay $330 per quarter for myself while United Healthcare still covers my spouse. Medicare does not cover my medical bills at the same level as United Healthcare, so United now pays only 80 percent of what Medicare didn’t cover. I must pay the rest.

My question is, can I be forced to enroll in Medicare? I only did it because the PA said I had to. I read somewhere that it is unconstitutional under New York State law to diminish retirement benefits. Would this apply to those in my situation? D.P.

Dear D.P: This is a very complicated situation. So I’ll quote directly from the Centers for Medicare & Medicaid Services, which I asked about your case.

The bottom line seems to be that it’s up to United Healthcare whether or not you are forced to enroll in Medicare at 65. But there’s hope: you might be eligible to be reimbursed for your costs. “Since the requirement to enroll in Medicare at age 65, if retired, is up to his private insurance, this question needs to be directed to the New York State Insurance Department,” said the center. The spokesman added: “In your reader’s case, as a NYS retiree, he may be mandated to enroll in Medicare but also entitled to reimbursement for the monthly Medicare Part B premium. He should check with his benefits administrator.”